System.NullReferenceException in mvc partial view when passing a list - asp.net-mvc

Question

I am trying to add a list in search box in partial view, but I am always getting System.NullReferenceException. A similar option is working when I keep as a separate view. I am not what I am doing wrong when passing List?
Following is the snippet from views and controllers:
1] _layout.cshtml:
<div class="row">
#Html.Partial("SearchBarPartial2", Model)
</div>
2] SearchPartialView2.cshtml:
<div class="form-group">
#using (Html.BeginForm("SearchBarPartial2", "Search"))
{
#Html.LabelFor(m => m.CompanyList, new { #class = "col-md-2 control-label" })
<div class="col-md-10">
#Html.DropDownListFor(
m => m.CompanyList,
new SelectList(Model.CompanyList, "fldt", "Value", Model.CompanyList.First().Value),
new { #class = "form-control" }
)
</div>
}
</div>
3] SearchController.cs:
public ActionResult SearchBarPartial2(cmpnytable cmpnytable1)
{
List<Company> objcompany = new List<Company>();
objcompany = GetCompanyList();
SelectList objlistofcompanytobind = new SelectList(objcompany, "ID", "Name", 0);
cmpnytable1.CompanyList = objlistofcompanytobind;
return View(cmpnytable1);
}

Answer 1

Your drop down list declaration already shown evidence of the error:
#Html.DropDownListFor(m => m.CompanyList, new SelectList(Model.CompanyList, "fldt", "Value", Model.CompanyList.First().Value), new { #class = "form-control" })
As Stephen said, you're assigned the model binding expression pointed to CompanyList, which becomes the source of all option tags to be rendered. It has no sense to pass the SelectList items as both binding target and source of the option list.
To resolve this issue, place additional model property with integer/string type for holding DropDownList selection result as this:
// Model
public class cmpnytable
{
// other properties here
public int SelectedId { get; set; }
}
// View
#model myproj.Models.cmpnytable
#Html.DropDownListFor(m => m.SelectedId, Model.CompanyList, new { #class = "form-control" })
Since CompanyList itself passed to view as SelectList, it's no use to create new instance of SelectList on the view.